Signal generation apparatus and linearity correction method thereof

ABSTRACT

There are provided a signal generation unit that generates a predetermined digital signal, a level conversion unit that converts a level of the digital signal generated by the signal generation unit, a DA converter that converts the digital signal of which the level is converted by the level conversion unit into an analog signal in a predetermined intermediate frequency bandwidth, and a control unit that creates correction data for correcting a linearity of a level of an output signal of the DA converter for all frequencies to be used, based on actual data which is data of a level of an actual output signal when a setting of the level of the output signal of the DA converter is changed at a predetermined level interval, at a predetermined frequency, and converts a level of an input signal of the DA converter with the correction data.

TECHNICAL FIELD

The present invention relates to a signal generation apparatus thatgenerates a modulated wave in a desired frequency bandwidth.

BACKGROUND ART

As a signal generation apparatus that generates a modulated wave in adesired frequency bandwidth, there is known, for example, a signalgeneration apparatus that generates a modulated wave in a desiredfrequency bandwidth by frequency-converting an intermediate frequencysignal generated by any signal generator with a mixer or the like.

Such a signal generation apparatus is incorporated in, for example, amobile terminal test device or the like that tests a mobilecommunication terminal, and generates and outputs a test signal.

Patent Document 1 describes a mobile terminal test system that changes asignal level of a signal output from a signal generator with anattenuator and transmits the signal to a measurement target terminal, inwhich a calibration value for each frequency value is acquired based oneach signal level in a case where a frequency of the signal output fromthe signal generator is sequentially changed.

RELATED ART DOCUMENT Patent Document

[Patent Document 1] JP-A-2003-18104

DISCLOSURE OF THE INVENTION Problem that the Invention is to Solve

However, in such a mobile terminal test system, the calibration value isacquired for each predetermined frequency, in an entire frequencybandwidth to be used, it takes time to acquire the calibration value.

Therefore, an object of the present invention is to provide a signalgeneration apparatus capable of creating correction data of allfrequencies to be used from data in a limited frequency range, andeasily correcting a linearity of a level of an output signal.

Means for Solving the Problem

According to an aspect of the present invention, there is provided asignal generation apparatus including: a signal generation unit thatgenerates any digital signal; a level conversion unit that converts alevel of the digital signal generated by the signal generation unit; aDA converter that converts the digital signal of which the level isconverted by the level conversion unit into an analog signal having apredetermined frequency; an amplifier that amplifies the analog signalconverted by the DA converter; a frequency conversion unit that convertsthe frequency of the analog signal amplified by the amplifier; acorrection data storage unit (15); and a control unit (17), in which theDA converter is configured to adjust a level of an output signal, thecontrol unit creates correction data for correcting a linearity of thelevel of the output signal of the DA converter, for all frequencies tobe used, based on actual data which is data of a level of an actualoutput signal at a predetermined frequency when a setting of the levelof the output signal of the DA converter is changed at a predeterminedlevel interval, and stores the created correction data in the correctiondata storage unit, and the control unit causes the level conversion unitto convert a level of an input signal of the DA converter with thecorrection data stored in the correction data storage unit.

With this configuration, based on the actual data which is the data ofthe level of the actual output signal at the predetermined frequencywhen the setting of the level of the output signal of the DA converteris changed at the predetermined level interval, the correction data forcorrecting the linearity of the level of the output signal of the DAconverter is created for all the frequencies to be used, and the levelof the input signal of the DA converter is converted with the correctiondata. Therefore, it is possible to easily correct the linearity of thelevel of the output signal.

Further, in the signal generation apparatus according to the presentinvention, the control unit causes the level conversion unit to convertthe level of the input signal of the DA converter with the correctiondata stored in the correction data storage unit only in a range in whichthe linearity of the level of the output signal of the DA converter ispoor.

With this configuration, the correction operation is performed only inthe range in which the linearity of the level of the output signal ofthe DA converter is poor. Therefore, it is possible to speed up thecorrection operation, and simplify the apparatus.

Further, in the signal generation apparatus according to the presentinvention, the control unit acquires the actual data only in a range inwhich the linearity of the level of the output signal of the DAconverter is poor, creates the correction data, and stores the createdcorrection data in the correction data storage unit.

With this configuration, the actual data is acquired only in the rangein which the linearity of the level of the output signal of the DAconverter is poor, and the correction data is created. Therefore, it ispossible to easily create the correction data.

Further, according to another aspect of the present invention, there isprovided a linearity correction method of a signal generation apparatusincluding a signal generation unit that generates any digital signal, alevel conversion unit that converts a level of the digital signalgenerated by the signal generation unit, a DA converter that convertsthe digital signal of which the level is converted by the levelconversion unit into an analog signal having a predetermined frequency,an amplifier that amplifies the analog signal converted by the DAconverter, a frequency conversion unit that converts the frequency ofthe analog signal amplified by the amplifier, and a correction datastorage unit (15), the method including: a step of acquiring actual datawhich is data of a level of an actual output signal at a predeterminedfrequency when a setting of a level of an output signal of the DAconverter is changed at a predetermined level interval; a step ofcreating correction data for correcting a linearity of the level of theoutput signal of the DA converter for all frequencies to be used, basedon the actual data, and storing the created correction data in thecorrection data storage unit; and a step of causing the level conversionunit to convert a level of an input signal of the DA converter with thecorrection data stored in the correction data storage unit.

Further, in the linearity correction method according to the presentinvention, in the step of converting the input signal of the DAconverter, the input signal of the DA converter is converted with thecorrection data stored in the correction data storage unit only a rangein which the linearity of the level of the output signal of the DAconverter is poor.

Further, in the linearity correction method according to the presentinvention, in the step of creating the correction data and storing thecreated correction data in the correction data storage unit, the actualdata is acquired only in a range in which the linearity of the level ofthe output signal of the DA converter is poor, the correction data iscreated, and the created correction data is stored in the correctiondata storage unit.

With this configuration, based on the actual data which is the data ofthe level of the actual output signal at the predetermined frequencywhen the setting of the level of the output signal of the DA converteris changed at the predetermined level interval, the correction data forcorrecting the linearity of the level of the output signal of the DAconverter is created for all the frequencies to be used, and the levelof the input signal of the DA converter is converted with the correctiondata. Therefore, it is possible to easily correct the linearity of thelevel of the output signal.

Advantage of the Invention

The present invention can provide a signal generation apparatus capableof creating correction data of all frequencies to be used from data in alimited frequency range, and easily correcting a linearity of a level ofan output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a signal generation apparatus according toan embodiment of the present invention.

FIG. 2 illustrates an example of a range of a frequency and a level tobe used by the signal generation apparatus according to the embodimentof the present invention, a range of a frequency and a level which needto be corrected, and a range of a frequency and a level for acquiringactual data.

FIG. 3 is a flowchart illustrating a procedure of a linearity correctionprocess of the signal generation apparatus according to the embodimentof the present invention.

FIG. 4 is a flowchart illustrating a procedure of a correction datacreation process of the signal generation apparatus according to theembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a signal generation apparatus according to an embodiment ofthe present invention will be described in detail with reference to thedrawings.

In FIG. 1 , a signal generation apparatus 1 according to the embodimentof the present invention includes a signal generation unit 10, a levelconversion unit 11, a digital to analog converter (DAC) 12, an amplifier(AMP) 13, a frequency conversion unit 14, a correction data storage unit15, an operation unit 16, and a control unit 17.

The signal generation unit 10 generates a predetermined digital signal.The level conversion unit 11 converts a signal level (gain) of a signalgenerated by the signal generation unit 10 and input as a digital signalto generate a digital signal. The DA converter 12 converts the digitalsignal converted by the level conversion unit 11 into an analog signalin a predetermined intermediate frequency bandwidth. The amplifier 13amplifies the analog signal converted by the DA converter 12. Thefrequency conversion unit 14 performs frequency-conversion on the analogsignal amplified by the amplifier 13 into an analog signal in apredetermined frequency bandwidth.

The correction data storage unit 15 is configured with a rewritablenon-volatile storage medium such as a flash memory. The correction datastorage unit 15 stores correction data for correcting the digital signalgenerated by the signal generation unit 10 with the level conversionunit 11.

The operation unit 16 includes input devices such as a keyboard, amouse, and a touch panel, and outputs information input by an operationto the control unit 17.

The control unit 17 is configured to include computer units including acentral processing unit (CPU), a random access memory (RAM), a read onlymemory (ROM), a hard disk device, and an input and output port (notillustrated).

The ROM and the hard disk device of this computer unit store variouscontrol constants, various maps, and the like, as well as a program forcausing the computer unit to function as the control unit 17. That is,the computer unit functions as the control unit 17 by the CPU executingthe program stored in the ROM and the hard disk device. The hard diskdevice may be a compact flash (CF) card by a flash memory.

The signal generation unit 10, the level conversion unit 11, the DAconverter 12, the amplifier 13, the frequency conversion unit 14, andthe operation unit 16 are connected to an input and output port of thecontrol unit 17, and the control unit 17 and each unit can transmit andreceive signals.

The signal generation apparatus 1 of the present embodiment can change alevel of an output signal. The level of the output signal of the signalgeneration apparatus 1 is changed by the DA converter 12 changing thelevel of the output signal. The DA converter 12 can adjust the level ofthe output signal.

In a case of adjusting the level of the output signal with the DAconverter 12, a linearity of the output level with respect to anadjustment amount of the level may not be desired due to a limit of aresolution of the DA converter 12, in some cases. In such a case, it isnecessary to correct a signal level of an input signal of the DAconverter 12 by the level conversion unit 11.

In a case of a configuration in which the DA converter 12 outputs ananalog signal in an intermediate frequency bandwidth and the frequencyconversion unit 14 converts a frequency as in the signal generationapparatus 1 of the present embodiment, a problem of the linearity ismainly due to an output performance of the DA converter 12, and theperformance of the DA converter 12 determines a performance of thesignal generation apparatus 1. Therefore, by acquiring data forcorrection at a limited frequency, the same effect as acquiring the dataat all frequencies can be expected.

Further, since a performance of the linearity is mainly the performanceof the DA converter 12, correction may be performed only in a range inwhich the linearity of the DA converter 12 is poor, for example, a rangein which a difference between an adjustment amount of the level and achange amount of the actual output level is equal to or larger than athreshold value. The range of the level to be corrected may bedetermined by a result of actual measurement or may be determined by acondition required for the output signal.

For this reason, in the signal generation apparatus 1 of the presentembodiment, as illustrated in FIG. 2 , at a frequency and a level atwhich linearity correction is required among frequencies and levels tobe used, based on actual data, which is data of a level of an outputsignal actually measured at a predetermined actual linearity dataacquisition frequency, correction is performed on all frequencies atwhich the linearity correction is required.

The DA converter 12 adjusts the level of the output signal by, forexample, adjusting an attenuation amount of the output signal. Theattenuation amount of the output signal by the DA converter 12 can beadjusted by a control of the control unit 17.

For example, a spectrum analyzer, a power meter, or the like formeasuring the level of the output signal of the signal generationapparatus 1 is connected to an output terminal of the signal generationapparatus 1, and a measurement result is output to the control unit 17,in a case of acquiring actual data at the actual linearity dataacquisition frequency.

Then, for example, by an operation to the operation unit 16, creation ofcorrection data is selected, and a frequency or a level range for theactual data acquisition is set.

When the creation of the correction data is selected by the operation tothe operation unit 16 and the frequency and the level range of actualdata acquisition is input, the control unit 17 acquires the actual data,and creates the correction data.

The control unit 17 generates, for example, an additive white Gaussiannoise (AWGN) signal in the signal generation unit 10, and changes anattenuation amount of the DA converter 12 within a set range, forexample, in 1 dB unit to acquire a measurement result of the level ofthe output signal at a set frequency.

From the acquired measurement result, the control unit 17 calculates aconversion value (correction amount) in the level conversion unit 11,for example, for each attenuation amount of the DA converter 12 so thatthe level of the output signal has a linearity, that is, a differencebetween a set attenuation amount and a attenuation amount of the actualoutput signal is equal to or less than a predetermined value.

The control unit 17 converts the calculated conversion value (correctionamount) at all frequencies and develops the resultant value, andcreates, for example, a table for determining the conversion value(correction amount) with the attenuation amount and the frequency, ascorrection data.

The control unit 17 stores the table of the created correction data inthe correction data storage unit 15, and applies the table so that thelevel conversion unit 11 corrects an input signal of the DA converter 12based on the correction data.

The actual measurement may be performed separately, and only data of themeasurement result may be input to the control unit 17 to create thecorrection data. In this case, all data of the level to be used may beinput to the control unit 17, and the control unit 17 may determine therange of the level at which the linearity correction is required.

A linearity correction process by the signal generation apparatus 1according to the present embodiment configured as described above willbe described with reference to FIG. 3 . A correction data creationprocess to be described below is started when creation of correctiondata is selected by an operation to the operation unit 16.

In step S1, the control unit 17 inputs ranges of a frequency and a levelfor actual data acquisition, and determines the input ranges of thefrequency and the level for the actual data acquisition as a linearitycorrection range. A parameter for determining the linearity correctionrange may be input to determine the linearity correction range. Afterexecuting the process in step S1, the control unit 17 executes theprocess in step S2.

In step S2, the control unit 17 acquires actual data in the determinedlinearity correction range by measurement. After executing the processin step S2, the control unit 17 executes the process in step S3.

In step S3, the control unit 17 creates a table of correction data basedon the acquired actual data. After executing the process in step S3, thecontrol unit 17 executes the process in step S4.

In step S4, the control unit 17 stores the created correction data inthe correction data storage unit 15, and applies the correction data.After executing the process in step S4, the control unit 17 ends thelinearity correction process.

Next, the correction data creation process in step S3 in FIG. 3 will bedescribed with reference to FIG. 4 .

In step S11, the control unit 17 calculates a correction amount for eachattenuation amount from the actual data of the measured linearitycorrection range. After executing the process in step S11, the controlunit 17 executes the process in step S12.

In step S12, the control unit 17 converts the calculated correctionamount for all frequencies to be used, and develops the correctionamount. After executing the process in step S12, the control unit 17executes the process in step S13.

In step S13, the control unit 17 uses the converted correction amount ascorrection data. After executing the process in step S13, the controlunit 17 ends the correction data creation process.

As described above, in the above-described embodiment, the control unit17 changes an attenuation amount of the DA converter 12 in apredetermined level unit within a set range, measures a level of anoutput signal at a set frequency, calculates a conversion value(correction amount) in the level conversion unit 11 from the measuredresult so that the level of the output signal of the DA converter 12 hasa linearity, converts and develops the calculated conversion value(correction amount) for all frequencies, creates a table for determininga conversion value (correction amount) with an attenuation amount and afrequency as correction data, store the created table of the correctiondata in the correction data storage unit 15, and applies the table sothat the level conversion unit 11 corrects an input signal of the DAconverter 12 with the correction data.

As a result, the correction data for all the frequencies to be used iscreated from the data in the limited frequency range, and the inputsignal of the DA converter 12 is corrected with the correction data.Therefore, it is possible to easily correct the linearity of the levelof the output signal.

In addition, even an inexpensive DA converter having a low resolutioncan generate a signal with a high-level accuracy.

Further, the control unit 17 corrects only a range in which thelinearity of the level of the output signal of the DA converter 12 ispoor.

As a result, the correction operation is performed only in the range inwhich the linearity of the level of the output signal of the DAconverter 12 is poor. Therefore, it is possible to speed up thecorrection operation, and simplify the apparatus.

Further, the control unit 17 acquires actual data only in the range inwhich the linearity of the level of the output signal of the DAconverter 12 is poor so as to create correction data.

As a result, the actual data is acquired only in the range in which thelinearity of the level of the output signal of the DA converter 12 ispoor, and the correction data is created. Therefore, it is possible toeasily create the correction data.

Although the embodiment of the present invention is disclosed, it isapparent that the embodiment can be modified by those skilled in the artwithout departing from the scope of the present invention. All suchmodifications and equivalents are intended to be included in thefollowing claims.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

1 Signal generation apparatus

10 Signal generation unit

11 Level conversion unit

12 DA converter

13 Amplifier

14 Frequency conversion unit

15 Correction data storage unit

16 Operation unit

17 Control unit

What is claimed is:
 1. A signal generation apparatus comprising: asignal generation unit that generates any digital signal; a levelconversion unit that converts a level of the digital signal generated bythe signal generation unit; a DA converter that converts the digitalsignal of which the level is converted by the level conversion unit intoan analog signal having a predetermined frequency; an amplifier thatamplifies the analog signal converted by the DA converter; a frequencyconversion unit that converts the frequency of the analog signalamplified by the amplifier; a correction data storage unit; and acontrol unit, wherein the DA converter is configured to adjust a levelof an output signal, the control unit creates correction data forcorrecting a linearity of the level of the output signal of the DAconverter, for all frequencies to be used, based on actual data which isdata of a level of an actual output signal at a predetermined frequencywhen a setting of the level of the output signal of the DA converter ischanged at a predetermined level interval, and stores the createdcorrection data in the correction data storage unit, and the controlunit causes the level conversion unit to convert a level of an inputsignal of the DA converter with the correction data stored in thecorrection data storage unit.
 2. The signal generation apparatusaccording to claim 1, wherein the control unit causes the levelconversion unit to convert the level of the input signal of the DAconverter with the correction data stored in the correction data storageunit only in a range in which the linearity of the level of the outputsignal of the DA converter is poor.
 3. The signal generation apparatusaccording to claim 1, wherein the control unit acquires the actual dataonly in a range in which the linearity of the level of the output signalof the DA converter is poor, creates the correction data, and stores thecreated correction data in the correction data storage unit.
 4. Alinearity correction method of a signal generation apparatus including asignal generation unit that generates any digital signal, a levelconversion unit that converts a level of the digital signal generated bythe signal generation unit, a DA converter that converts the digitalsignal of which the level is converted by the level conversion unit intoan analog signal having a predetermined frequency, an amplifier thatamplifies the analog signal converted by the DA converter, a frequencyconversion unit that converts the frequency of the analog signalamplified by the amplifier, and a correction data storage unit, themethod comprising: a step of acquiring actual data which is data of alevel of an actual output signal at a predetermined frequency when asetting of a level of an output signal of the DA converter is changed ata predetermined level interval; a step of creating correction data forcorrecting a linearity of the level of the output signal of the DAconverter for all frequencies to be used, based on the actual data, andstoring the created correction data in the correction data storage unit;and a step of causing the level conversion unit to convert an inputsignal of the DA converter with the correction data stored in thecorrection data storage unit.
 5. The linearity correction methodaccording to claim 4, wherein in the step of converting the input signalof the DA converter, the input signal of the DA converter is convertedwith the correction data stored in the correction data storage unit onlya range in which the linearity of the level of the output signal of theDA converter is poor.
 6. The linearity correction method according toclaim 4, wherein in the step of creating the correction data and storingthe created correction data in the correction data storage unit, theactual data is acquired only in a range in which the linearity of thelevel of the output signal of the DA converter is poor, the correctiondata is created, and the created correction data is stored in thecorrection data storage unit.